. The organism stains blue in giemsa’s stain. . Grow in yolk sac of embryonated eggs, cell culture and laboratory animals. . Destroyed by heat, drying and bactericidal chemicals. Antigenic structure: Group-specific antigens Species-specific antigens Clinical Features: Clinical illness is due to the invasion and multiplication of rickettsiae in the endothelial cells of small blood
vessels. It manifests with fever, enlargement of liver and spleen.
headache, malaise, skin rash and
The genus rickettsiae has three main groups based on their antigenic structure. These are: Typhus group
Scrub typhus group Spotted fever group
Table 2.8. Hosts and vectors of the medically important rickettsiae
Organism 1. Typhus group R. prowazeckii R. typhi 2. Scrub typhus R. tsutsugamushi 3. Spotted fever group Disease Louse-borne typhus Murine typhus scrub typhus
African tick typhus